By ROBERT D. HERSHEY Jr., Special to the New York Times

Published: February 26, 1987

A herculean $45 million effort has reapportioned the Consumer Price Index's basket of goods and services to reflect a decade's worth of changes in the nation's spending patterns.

''What it does,'' Patrick C. Jackman, an official of the Labor Department, said of the revision, ''is update people's expenditure patterns from the 70's to the 80's.''

The revision, which is to be formally introduced on Friday when the index figures for January are released, will directly or indirectly affect almost every American household, or ''consumer unit,'' the term now preferred by the statisticians.

Among other uses, the index is the basis for changes in payments to 38 million Social Security beneficiaries, 20 million food stamp recipients, more than four million workers covered by contracts with escalator clauses and millions of Federal retirees.

The index also affects income tax brackets and the cost of school lunches for 23 million children. In the private sector, it influences a variety of payments, such as for royalties, alimony and child support. Service Sector Expands

The latest revision - the first since 1978 - records at least one momentous change. For the first time, the service sector accounts for more than half of all spending - 52 percent in 1982-1984, up from about 46 percent in 1972-1973. Spending on commodities and goods has slipped to 48 percent.

One implication of this now well-established trend, economists say, is that wages, fees and salaries will be the dominant influence on future inflation levels.

Other changes in the price index reflect the increased numbers of two-earner families and elderly people; more spending on physical fitness; new products such as compact disk stereo equipment; the impact of energy conservation, and the population gains of the Sun Belt.

Although the index is often referred to as a measure of the cost of living, it measures only the price of a basket of goods and services in a mix that must be periodically adjusted. If consumers change their buying habits because, say, the price of gasoline rises sharply or certain types of food decline in popularity, the market basket must be changed to keep the index a reliable barometer of the overall price level.

To aid in making comparisions, for the next six months the index will be calculated using both the old and new baskets.

Among the index's categories, food has shown a substantial long-term decline in relative importance. In 1939, food and beverages accounted for more than one-third of the market basket; under the latest revision, food fell to 17.8 percent, from 19.9 percent based on average spending during the previous measuring period.

The latest revision reflects a decline in consumption of red meat, but increased popularity for poultry. Even so, beef remained ''the meat of choice'' although many consumers have substituted ground beef for roasts.

The sugar and sweets component has also fallen sharply, a change attributed to health-consciousness and to shifts in the age mix of the population. Children and teen-agers are the biggest buyers of confectionery products, and the trend toward smaller families reduces the importance of these items in family budgets, analysts at the department explained.

That population trend also altered meal patterns. With fewer children, there is a decline in school lunches, so dinners-away-from-home rose in importance relative to lunches-away-from-home. That occurred despite the rise in the number of two-earner families in which women were eating lunch away from home.

The weighting for transportation fell almost three percentage points, to 18.7 percent of spending. A significant factor there was a decline in the number of miles driven and a rise in the fuel efficiency of vehicles. Those factors produced a 23.2 percent drop in gasoline consumption per consumer unit during the decade, the department reported.

Consumers were also keeping cars longer, but that did not raise proportional spending for repair and maintenance bills. Factors cited include improvements in car quality, such as better protection against corrosion; the 55-mile-an-hour speed limit and more do-it-yourself maintenance.

A component that did post a significant rise during the decade was housing - to 42.6 percent, from 37.7 percent based on average spending in the previous period. This was caused mainly by an increase in rents, the department said.

The share of spending devoted to medical care fell slightly, to 4.8 percent, a seeming anomaly for a category that has seen sharp rises in actual prices. The key factor here is who pays -a large part of health costs are borne by employee-benefit plans or by the Government and such payments are not reflected in the Consumer Price Index. That makes the index particularly misleading as a gauge of the cost of medical care.

Over all, the new index, covering 1982-84 spending patterns, is already somewhat out of date, even though the monthly price changes themselves will, of course, be current. BEHIND THE NEW PRICE MEASUREMENT Annual expenditures by urban consumer units in the seven major categories and selected subcategories for the Consumer Price Index. Many factors contributed to the need for revision, including differences in consumer buying habits as well as prices, population shifts in age and location, new technology and products, and new category definitions.* Former Revised Expenditure Average Relative Average Relative Category Expenditure Importance Expenditure Importance ALL ITEMS $22,065.00 100.000 $19,362.65 100.000 Food and beverages 4,380.12 19.851 3,454.36 17.840 Food at home 2,776.44 12.583 1,962.94 10.138 Food away from home 1,352.14 6.128 1,189.82 6.145 Alcoholic beverages 239.85 1.087 301.60 1.558 Housing 8,318.95 37.702 8,255.57 42.637 Residential rent 1,367.59 6.198 1,099.66 5.679 Homeowners' 'rent'** 3,029.08 13.728 3,519.20 18.175 Apparel and upkeep 1,116.71 5.061 1,263.23 6.524 Transportation 4,772.88 21.631 3,620.03 18.696 New vehicles 851.49 3.859 1,064.36 5.497 Used vehicles 1,014.77 4.599 246.08 1.271 Motor fuel 1,215.34 5.508 929.49 4.800 Public transportation 347.97 1.577 269.67 1.393 Medical care 1,383.25 6.269 928.58 4.796 Entertainment 931.58 4.222 848.02 4.380 Other goods and services 1,173.64 5.319 992.85 5.128 *A consumer unit is a household, individual or group of individuals that form an economically interdependent unit. Formerly, a unit was 2.8 persons; revised, it is 2.6. **What an unfurnished home could be expected to rent for, excluding utilities. Source: Bureau of Labor Statistics The New Consumer Profile Changes in demographic characteristics of urban consumer units in calculation of the Consumer Price Index.* Former Revised Income of consumer unit, before taxes $12,332 $23,183 Per capita income, before taxes $4,404 $8,917 Size of consumer unit (persons) 2.8 2.6 Number of earners 1.3 1.4 Number of children 1.0 .7 Age of reference person** 47.3 46.2 Sex of reference person: Male 75.9% 66.5% Sex of reference person: Female 24.1% 33.5% Percent reporting homeownership 55.8% 59.5% *A consumer unit is a household, individual or group of individuals that form an economically interdependent unit. **The person first mentioned by respondents in the consumer price survey when asked ''the name of the person or one of the persons who owns or rents'' the home. Source: Bureau of Labor Statistics

Correction: March 5, 1987, Thursday, Late City Final Edition Revised tables, with clarifications and an explanatory article, appear today on page D8.